Rebar coupler

ABSTRACT

Proposed is a rebar coupler including a housing formed by coupling a pair of housing bodies to each other and a plurality of coupling pieces positioned inside the housing and configured to fasten a rebar. The coupling piece includes an outer surface having a first protruding region, a second protruding region, and a first concaved region, and includes an inner surface having serrated protrusions configured to prevent the rebars from being moved in an opposite direction of an insertion direction. The housing body has concaved spaces such that symmetrical hollows are formed at the opposite sides of the housing, and rebar inlet ports are formed at opposite ends of the housing. A pair of the coupling pieces is positioned at the hollows such that the inner surfaces of the coupling pieces face each other, and the first end portions of the coupling pieces are configured to fasten the rebars.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2021-0052248, filed Apr. 22, 2021, the entire contents of which is incorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a rebar coupler capable of enabling a worker to easily couple rebars to each other regardless of a skill level and capable of reducing a construction time of coupling the rebars, the rebar coupler also having an excellent fastening strength.

Description of the Related Art

For construction and civil engineering structures, a rebar is used as a tensile member so as to reinforce tensile stress of concrete that is a compressive member. That is, a mold for configuring a girder, a wall, a column, and so on of a building is installed according to a construction drawing, rebars are arranged in the mold and concrete is poured, and then the poured concrete is cured for a predetermined period and the mold is removed, whereby construction of a reinforced concrete structure is completed.

The arranged rebars receive tensile stress or compressive stress caused by bending moment, and a length of the rebar is produced in a uniform standard that is approximately 3.5 m to 10 m. Therefore, when the length of the rebar is shorter than a width and a height of the mold, a plurality of rebars is required to be connected to each other so as to arrange the rebar in the mold, so that various techniques for coupling rebars to each other have been developed.

As a coupling method of connecting rebars, there are a lap joint method, a gas pressure welding joint method, a coupler joint method, and so on.

The lap joint method is a method of connecting rebars by overlapping the rebars to each other and winding a binding wire such as a steel wire around multiple places on the rebars, and applying of the lap joint method is limited to couple the rebars having small diameters, and there is a disadvantage that the coupling may be separated by the pouring of concrete or by a working load.

The gas pressure welding joint method is a method of coupling the rebars by heating cross-sections of the rebars with flame and then coupling the rebars to each other by mechanically pressing the rebars, and is sensitive to climatic conditions. Further, since a coupling quality of the rebars may be significantly affected depending on a skill level of a worker, there may be limitations in homogeneity and constructability of performing the gas pressure welding joint method.

In addition, in the coupler joint method in which a thread is formed on the rebar to be connected and the thread formed on an end portion of the rebar is fastened to a coupler on which a female-thread is formed, a loss of the rebar may occur on a cross-section of the rebar, and a tap processing may consume a significant portion of a cost and a significant portion of a time. To overcome this, techniques such as Korean Patent No. 10-1959076, “REBAR COUPLER” and Korean Patent No. 10-1845850, “STEEL REINFORCEMENT COUPLER OF ONE-TOUCH TYPE ENABLE TO CHECK INSERTION DEPTH OF STEEL REINFORCEMENT” have been disclosed.

Document of Related Art

-   (Patent literature 1) Korean Patent No. 10-1959076 (registration     date: Mar. 11, 2019) -   (Patent literature 2) Korean Patent No. 10-1845850 (registration     date: Mar. 30, 2018)

SUMMARY OF THE INVENTION

Accordingly, the present disclosure has been made keeping in mind the above problems occurring in the related art, and an objective of the present disclosure is to provide a rebar coupler capable of enabling a worker to easily couple rebars regardless of a skill level and capable of reducing a construction time of coupling the rebars, the rebar coupler also having an excellent fastening strength.

The objectives that can be obtained from the present disclosure are not limited to the above-mentioned objectives, and other objectives not mentioned herein will be clearly understood by those skilled in the art from the following description.

In order to achieve the above objective, according to one aspect of the present disclosure, there is provided a rebar coupler including: a housing formed by coupling a pair of housing bodies to each other; and a plurality of coupling pieces positioned inside the housing and configured to fasten rebars to each other, wherein each of the coupling pieces may include: an outer surface in which a first protruding region and a second protruding region are provided by being arranged in a direction from a first end portion to a second end portion of the coupling piece, with a first concaved region formed between the first and second protruding regions; and an inner surface provided with serrated protrusions such that an associated rebar inserted into the housing from the first end portion of the coupling piece is prevented from being moved in a direction opposite to an insertion direction of the rebar, wherein each of the housing bodies may be provided with concaved spaces that are respectively positioned at opposite sides of the housing body from a center of a longitudinal direction of the housing body such that hollows symmetrical to each other with respect to the center of the longitudinal direction of the housing body are respectively formed at the opposite sides of the housing, and rebar inlet ports may be respectively formed at opposite end portions of the housing, and a pair of the coupling pieces may be positioned at each of the hollows such that the inner surfaces of the coupling pieces face each other, and the first end portions of the coupling pieces may be positioned at inner sides of the rebar inlet ports of the housing such that the rebars inserted into the housing are fastened.

Each of the housing bodies may include a pair of first steps positioned at the opposite sides of the housing body from the center of the longitudinal direction of the housing body, the pair of first steps being configured such that end portions of the rebars inserted into the housing from the respective rebar inlet ports positioned at the opposite end portions of the housing are in contact with and are seated on the pair of first steps.

Each of the housing bodies may include: a pair of second steps respectively provided along directions from the first steps toward the rebar inlet ports at the opposite end portions of the housing; and springs respectively interposed between the second end portions of the coupling pieces and the second steps.

Each of the housing bodies may be provided with opening portions where the respective springs are partially exposed, the opening portions being configured such that respective end portions of the second steps become respective first side surfaces of the opening portions.

Each of the housing bodies may be configured such that an inner portion thereof is provided with coupling piece seating portions that are formed in shapes corresponding to the outer surfaces of the coupling pieces, and the first end portions of the coupling pieces may be respectively positioned on the coupling piece seating portions and may be respectively arranged in directions toward the rebar inlet ports of the housing.

When each of the coupling pieces is viewed in cross-section, from the first end portion of the coupling piece to the second end portion of the coupling piece, the first protruding region may be provided with a first inclined portion having a predetermined angle in an outside direction, a first horizontal portion extending from the first inclined portion in a horizontal direction, and a second inclined portion extending from the first horizontal portion and having a predetermined angle in an inside direction.

Each of the housing bodies may be configured such that third steps are respectively provided at the inner sides of the rebar inlet ports, and a space where the first inclined portion of the coupling piece and an associated third step are not engaged with each other when the first end portion of the coupling piece and the third step are in contact with each other may be formed between the first inclined portion of the coupling piece and the third step.

When an angle between the first inclined portion and an extending line directing toward a first end portion of the horizontal portion is referred to as θ, a horizontal length of the first inclined portion is referred to as a, and a height of each of the serrated protrusions of the inner surface of the coupling piece is referred to as n, the first inclined portion of the coupling piece and the serrated protrusions of the inner side of the coupling piece may satisfy a relational expression 1 that is described below.

a×tan θ≥1.1×n   Relational expression (1)

The second protruding region may be configured to have a third inclined portion having a predetermined angle in the outside direction toward the second end portion of the coupling piece, and a second horizontal portion extending from the third inclined portion in the horizontal direction.

The rebar coupler may satisfy the relational expression 1 that is described below.

a×tan θ≥1.1×n   Relational expression (1)

Where n is a height of each of the serrated protrusions and a is a largest value among a horizontal length of the first inclined portion, a horizontal length of the third inclined portion, and a horizontal length of an inclined portion of a wall surface of a coupling piece seating portion corresponding to the third inclined portion.

When a horizontal length of the first inclined portion is referred to as a, a sum of a length of the first horizontal portion and half of a horizontal length of the second inclined portion is referred to as b, a sum of half of the horizontal length of the second inclined portion and a length of the first concaved region is referred to as c, a horizontal length of the third inclined portion is referred to as a′, and a length of the second horizontal portion is referred to as b′, the protruding regions and the first concaved region of each of the coupling pieces may satisfy a relational expression 2 that is described below.

a+a′>0.1(b+c+b′)   Relational expression (2)

By using the rebar coupler according to an embodiment of the present disclosure, the worker may easily couple the rebars regardless of skill level, thus there are advantages that construction time of coupling the rebars is reduced. Another advantage of the present disclosure resides in that the rebar coupler has an excellent fastening strength.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objectives, features, and other advantages of the present disclosure will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

FIGS. 1A and 1B are perspective views illustrating a housing body of a rebar coupler according to an embodiment of the present disclosure;

FIG. 2 is a perspective view illustrating a coupling piece of the rebar coupler according to an embodiment of the present disclosure;

FIG. 3 is a perspective view illustrating a spring of the rebar coupler according to an embodiment of the present disclosure;

FIG. 4A is a perspective view illustrating a defect of rebar coupling occurring in a rebar coupler;

FIG. 4B is a cross-sectional plan view taken along line I-I′ in FIG. 4A;

FIG. 5A is a perspective view illustrating coupling of the rebar coupler according to an embodiment of the present disclosure;

FIG. 5B is a cross-sectional plan view taken along line

in FIG. 5A;

FIG. 6 is a cross-sectional view illustrating coupling of a rebar and the rebar coupler according to an embodiment of the present disclosure;

FIG. 7 is a cross-sectional view illustrating the coupling piece of the rebar coupler according to an embodiment of the present disclosure;

FIG. 8 is a cross-sectional view illustrating a setting of a welding coupling region of the rebar coupler according to an embodiment of the present disclosure; and

FIG. 9 is a cross-sectional view illustrating the coupling piece and the housing body according to another embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings. The following embodiments are provided by way of example so as to fully convey the spirit of the present disclosure to those skilled in the art. Accordingly, the present disclosure is not limited to the embodiments disclosed herein and can also be implemented in different forms. In addition, in the drawings, the length, the thickness and the like of layers and areas may be exaggerated for convenience. Like reference symbols denote like elements throughout the specification.

FIGS. 1A and 1B are perspective views illustrating a housing body of a rebar coupler according to an embodiment of the present disclosure. FIG. 2 is a perspective view illustrating a coupling piece of the rebar coupler according to an embodiment of the present disclosure. FIG. 3 is a perspective view illustrating a spring of the rebar coupler according to an embodiment of the present disclosure. FIG. 4A is a perspective view illustrating defect of rebar coupling occurring in a rebar coupler. FIG. 4B is a cross-sectional plan view taken along line I-I′ in FIG. 4A. FIG. 5A is a perspective view illustrating coupling of the rebar coupler according to an embodiment of the present disclosure. FIG. 5B is a cross-sectional plan view taken along line

in FIG. 5A. FIG. 6 is a cross-sectional view illustrating coupling of a rebar and the rebar coupler according to an embodiment of the present disclosure. FIG. 7 is a cross-sectional view illustrating the coupling piece of the rebar coupler according to an embodiment of the present disclosure. FIG. 8 is a cross-sectional view illustrating a setting of a welding coupling region of the rebar coupler according to an embodiment of the present disclosure. FIG. 9 is a cross-sectional view illustrating the coupling piece and the housing body according to another embodiment of the present disclosure.

In the present disclosure, referring to FIGS. 1A to 9, there is provided a rebar coupler 10 including: a housing formed by coupling a pair of housing bodies 200 to each other; and a plurality of coupling pieces 100 positioned inside the housing and configured to fasten rebars 20 to each other. Each of the coupling pieces 100 may include: an outer surface 101 in which a first protruding region 110 and a second protruding region 120 are provided by being arranged in a direction from a first end portion to a second end portion of the coupling piece 100, with and a first concaved region 130 formed between the first and second protruding regions 110 and 120; and an inner surface 102 provided with serrated protrusions 102 t such that an associated rebar 20 inserted in to the housing from the first end portion of the coupling piece 100 is prevented from being moved in a direction opposite to an insertion direction of the rebar 20. Each of the housing bodies 200 may be provided with concaved spaces that are respectively positioned at opposite sides of the housing body 200 from a center of a longitudinal direction of the housing body 200 such that hollows 220 symmetrical to each other with respect to the center of the longitudinal direction of the housing body 200 are respectively formed inside opposite sides of the housing, and rebar inlet ports 210 may be respectively provided at opposite end portions of the housing. A pair of the coupling pieces 100 may be positioned at each of the hollows 200 of the housing such that the inner surfaces 102 of the pair of coupling pieces 100 face each other, and the first end portions of the coupling pieces 100 may be positioned at inner sides of the rebar inlet ports 210 of the housing and may be configured to fasten the rebars 20 inserted into the housing.

A material of the rebar 20 may be any one of SD300, SD400, SD500, SD600, SD700, SD400 S, SD500 S, and SD600 S that are rod steels for a reinforced concrete defined in KS D 3504. The rebar coupler 10 is manufactured from a material having higher yield strength than a yield strength of a material of the rebar 20. For example, the material of the rebar coupler 10 of the present disclosure may be any one of SM10C, SM12C, SM15C, SM17C, SM20C, SM22C, SM25C, SM28C, SM30C, SM33C, SM35C, SM38C, SM40C, SM43C, SM45C, SM487C, SM50C, SM53C, SM55C, SM58C, SM9CK, SM15CK, and SM20CK that are carbon steels for a machine structural use defined in KS D 3752. In addition, as another example, the material of the rebar coupler 10 of the present disclosure may be any one of SCM415, SCM420, SNCM220, SNCM420, and SNCM439. In an embodiment of the present disclosure, SM45C steel was used.

In detail, each of the housing bodies 200 may have the concaved spaces respectively positioned at the opposite sides of the housing body 200 from the center of the longitudinal direction of the housing body 200 such that the hollows 220 symmetrical to each other with respect to the center of the longitudinal direction of the housing body 200 are respectively formed inside the opposite sides of the housing. Further, the rebar inlet ports 210 may be respectively provided at the opposite end portions of the housing, and respective end portions of the rebars 20 may be respectively inserted into the hollows 220 from the rebar inlet ports 210 respectively positioned at the opposite sides of the housing. That is, the concaved spaces respectively provided at the housing body 200 and symmetrical to each other from the center of the housing body 200 may be formed into the hollows 220 by coupling the pair of housing bodies 200. Accordingly, the housing may be provided with two hollows 220 which are in communication with respective rebar inlet ports 210 and which are symmetrical to each other from the center of the housing. In other words, a housing sectional surface 280 formed at a center axis of the housing and formed along a longitudinal direction of the rebar 20 may be a coupling surface 280 to which the housing bodies 200 are coupled.

As illustrated in FIGS. 6 and 7, the coupling piece 100 may include: the outer surface 101 in which the first protruding region 110 and the second protruding region 120 are provided by being arranged in the direction from the first end portion to the second end portion of the coupling piece 100, with the first concaved region 130 formed between the first and second protruding regions 110 and 120; and the inner surface 102 provided with the serrated protrusions 102 t such that the associated rebar 20 inserted into the housing from the first end portion of the coupling piece 100 is prevented from being moved in the direction opposite to the insertion direction of the rebar 20. The pair of coupling pieces 100 may be positioned at each of the hollows 220 of the housing such that the inner surfaces 102 of the pair of coupling pieces 100 face each other, so that the pair of coupling pieces 100 is provided at the inside of each of the opposite end portions of the housing. Further, the first end portions of the coupling pieces 100 may be positioned at the inner sides of the rebar inlet ports 210 and may be configured to fasten the rebars 20 inserted into the housing.

That is, since the coupling piece 100 includes the inner surface 102 provided with the serrated protrusions 102 t, the rebar 20 inserted from the first end portion of the coupling piece 100 may be prevented from being moved in the direction opposite to the insertion direction of the rebar 20. In this case, each of the serrated protrusions 102 t is formed by communicating and combining a circular arc shape 102 a formed as a quarter of a circular arc and a parabola shape 102 b formed as a half of a parabola. Further, the parabola shapes 102 b are positioned along the insertion direction, so that snagging of rebar nodes 25 that occurs when the rebar 20 is inserted may be minimized. In addition, the circular arc shapes 102 a corresponding to a protrusion height of each of the rebar nodes 25 are positioned along the direction opposite to the insertion direction, so that the circular arc shapes 102 a may function as jaws that prevent the rebar 20 from being moved in a direction toward outside of the housing after the rebar 20 is inserted.

Each of the housing bodies 200 may include a pair of first steps 230 positioned at the opposite sides of the housing body 200 from the center of the longitudinal direction of the housing body 200 and on which the end portions of each of the rebars 20 inserted from the respective rebar inlet ports 210 are in contact with and seated, so that positions of the rebars 20 inserted into the housing may be fixed.

Furthermore, each of the housing bodies 200 may include a pair of second steps 250 respectively positioned along directions from the first steps 230 toward the rebar inlet ports 210 that are respectively positioned at the opposite end portions of the housing body 200, and springs 300 may be respectively interposed between the second end portions of the coupling pieces 100 and the second steps 250. That is, the rebar 20 may pass through an inside of the spring 300 that is configured such that a first end portion thereof is in contact with the second step 250, and the end portion of the rebar 20 may be in contact with the first step 230 and may be seated on the first step 230. During performing a process of inserting the rebar 20 in the housing, the rebar nodes 25 are in contact with the serrated protrusions 102 t of the coupling piece 100 and friction is acting on the rebar nodes 25, and the second end portion of the coupling piece 100 is in contact with the spring 300 and is fixed by receiving a repulsive force of the spring 300 in a direction opposite to the insertion direction of the rebar 20. Due to the repulsive force, the coupling piece 100 may be positioned at a coupling piece seating portion 260 that will be described later.

In the housing body 200, opening portions 240 where the respective springs 300 are partially exposed may be formed such that the end portions of the second steps 230 become first side surfaces of the opening portions 240, and a position of the rebar 20 that is being inserted through the spring 300 may be checked via the opening portion 240.

Further, the coupling piece seating portions 260 formed in shapes corresponding to the outer surfaces 101 of the coupling pieces 100 may be formed inside the housing body 200, and the first end portions of the coupling pieces 100 may be respectively positioned at the coupling piece seating portions 260 and may be respectively arranged in directions toward the rebar inlet ports 210 of the housing. That is, the coupling piece insertion portion 260 may be formed in a shape corresponding to the outer surface 101 of the coupling piece 100 in which the first protruding region 110 and the second protruding region 120 are provided by being arranged in a direction from the first end portion to the second end portion of the coupling piece 100, with the first concaved region 130 formed between the first and second protruding regions 110 and 120. Further, a wall surface 262 of the coupling piece seating portion 260 may be provided with a curved area formed in a shape corresponding to the outer surface 101 of the coupling piece 100, and a bottom surface 264 of the coupling piece seating portion 260 may be provided with a concaved groove formed in a shape corresponding to a cross-section of the coupling piece 100. That is, by coupling the pair of housing bodies 200 together, the wall surfaces 262 of the coupling piece seating portions 260 are coupled together, and a wall surface concaved portion that corresponds to the entire shape of the outer surface 101 of the coupling piece 100 may be formed. Accordingly, in the hollows 220, the pair of coupling pieces 100 may be positioned to be symmetrical to each other around the rebars 20.

When each of the coupling pieces 100 is viewed in cross-section, from the first end portion of the coupling piece 100 to the second end portion of the coupling piece 100, the first protruding region 110 may include: a first inclined portion 111 having a predetermined angle θ in an outside direction; a first horizontal portion 113 extending from the first inclined portion 111 in a horizontal direction; and a second inclined portion 115 extending from the first horizontal portion 113 and having a predetermined angle in an inside direction.

In this case, in each of the housing bodies 200, third steps 270 may be respectively provided at the inner sides of the rebar inlet ports 210. Further, a space S where the first inclined portion 111 and the third step 270 are not engaged with each other when the first end portion of the coupling piece 100 and the third step 270 are in contact with each other may be formed between the first inclined portion 111 and the third step 270. That is, as illustrated in FIG. 5B, a part 266 of the wall surface of the coupling piece seating portion 260 corresponding to the first inclined portion 111 of the coupling piece 100 while the first end portion of the coupling piece 100 and the third step 270 are in contact with each other may be formed to be spaced apart from the first inclined portion 111.

FIG. 4A is a view illustrating a defect of rebar coupling that occurred in coupling of a rebar and a rebar coupler. As illustrated in FIG. 4B, when an inner side surface of an inlet port of a housing and an outer circumferential surface of a first end portion of a coupling piece are in contact with each other and are positioned at a position A, a defect in which a welded portion of a coupled area of the housing body 200 is opened (cracked) may occur as illustrated in FIG. 4A. This situation is expected to be due to thermal expansion characteristics or thermal contraction characteristics of the housing body 200, the coupling piece 100, and a welding material. However, as illustrated in FIG. 5B that illustrates the rebar coupler 10 of the present disclosure, the space S is secured between the inside of the rebar inlet port 210 and the first end portion of the coupling piece 100, so that it is possible to increase a resistance to breakage of a minimum welding region D since a free space with respect to thermal expansion or thermal contraction is provided, and it is possible to maintain a coupling quality as illustrated in FIG. 5A by preventing the defect in which the welded portion is opened.

When an angle between the first inclined portion 111 and an extending line directing a first end portion of the first horizontal portion 113 is referred to as (θ), a horizontal length of the first inclined portion 111 is referred to as (a), and a height of each of the serrated protrusions 102 t of an inner side surface of the coupling piece 100 is referred to as (n), the first inclined portion 111 and serrated protrusions 102 t of the coupling piece 100 may satisfy a relational expression (1) that is described below.

a×tan θ≥1.1 ×n   relational expression (1)

When a height (a·tan θ) of the first inclined portion 111 may be at least 1.1 times larger than the height (n) of the serrated protrusions 102 t of the inner side surface of the coupling piece 100, a sufficient fastening force between the rebar 20 and the coupling piece 100 and a sufficient fastening force between the coupling piece 100 and the housing may be secured. Further, it is more preferable that the height (a·tan θ) of the first inclined portion 111 is at least 1.1 times and less than 1.5 times larger than the height (n) of the serrated protrusions 102 t of the inner side surface of the coupling piece 100.

In the relational expression (1), (a) is limited to the horizontal length of the first inclined portion 111. However, since the horizontal length of the first inclined portion 111, a horizontal length (a′) of a third inclined portion 121, and a horizontal length (a″) of an inclined portion of the wall surface 262 of the coupling piece seating portion 260 corresponding to the third inclined portion 121 when the second protruding region 120 is retreated to the maximum are formed such that sizes thereof are corresponding to each other, (a) in the relational expression (1) is the most largest value among the horizontal length (a) of the first inclined portion 111, the horizontal length (a′) of the third inclined portion 121, and the horizontal length (a″) of the inclined portion of the wall surface 262 of the coupling piece seating portion 260 corresponding to the third inclined portion 121.

The fastening force is an evaluation item for measuring a coupling force of a rebar coupler by performing a one-way tensioning test, and is evaluated by a test method of KS D 0249. As a test piece used to measure the fastening force, the rebar coupler of the present disclosure in which two axes of respective rebars are connected to each other is used. That is, after the rebar coupler is assembled and welded, two rebars are inserted into and fastened to the rebar coupler as illustrated in FIG. 6. The fastening force of the rebar coupler may be at least 125% of yield strength of a base material of the rebar.

TABLE 1 Fastening force in comparison a · tanθ with rebar yield strength 0.9 n  12% 1.0 n  90% 1.1 n 125% 1.2 n 130% 1.3 n 140%

As shown in Table 1, when the height (a·tan θ) of the first inclined surface 111 is at least 1.1 times larger than the height (n) of the serrated protrusions 102 t of the inner side surface of the coupling piece 100, it can be confirmed that the fastening force of the rebar coupler is at least 125% of the yield strength of the base material of the rebar. However, when the height (a·tan θ) of the first inclined surface 111 is at least 1.5 times larger than the height (n) of the serrated protrusions 102 t of the inner side surface of the coupling piece 100, there is a limitation of realizing a slim design of a product, so that it is preferable that the height (a·tan θ) of the first inclined surface 111 is less than 1.5 times larger than the height (n) of the serrated protrusions 102 t of the inner side surface of the coupling piece 100.

For example, the angle (θ) between the first inclined portion 111 and the extending line directing the first end portion of the first horizontal portion 113 and the angle between the third inclined portion 121 of the second protruding region 120 and an extending line directing a first end portion of the second horizontal portion 123 may be the same.

Meanwhile, in relation to realize the slim design of the rebar coupler 10, the angle (θ) of the first inclined portion 111 of the coupling piece 100 and the horizontal length (a) of the first inclined portion 111 are linked to each other. For example, as the angle (θ) of the first inclined portion 111 increases, the horizontal length (a) of the first inclined portion 111 decreases. In addition, from the relational expression (1), when the height (a·tan θ) of the first inclined portion 111 is provided to be at least 1.1 times larger than the height (n) of the serrated protrusions 102 t of the inner side surface of the coupling piece 100, the fastening force increases, but the size of the rebar coupler 10 may also increase.

Meanwhile, the protruding regions 110 and 120 of the coupling piece 100 and the first concaved region 130 may satisfy a relational expression (2) that is described below.

a+a′>0.1(b+c+b′)   Relational expression (2)

For example, when the second protruding region 120 is provided with the third inclined portion 121 having a predetermined angle in the outside direction toward the second end portion of the coupling piece 100 and is provided with the second horizontal portion 123 extending from the third inclined portion 121 in the horizontal direction, and when the horizontal length of the first inclined portion 111 is referred to as (a), sum of the length of the first horizontal portion 113 and half of a horizontal length of the second inclined portion 115 is referred to as (b), sum of half of the horizontal length of the second inclined portion 115 and the horizontal length of the first concaved region 130 is referred to as (c), the horizontal length of the first inclined portion 121 is referred to as (a′), and a length of the second horizontal portion 123 is referred to as (b′), the protruding regions 110 and 120 and the first concaved region of each of the coupling pieces 100 may satisfy the relational expression (2). Further, it is preferable that a value of a+a′ exceeds 0.1(b+c+b′) and is less than 0.5(b+c+b′).

When a total length (b+c+b′) of a horizontal region of the outer side surface of the coupling piece 100 and a length (a+a′) of an inclined region of the outer side surface of the coupling piece 100 satisfy the relational expression (2), the housing may maintain the fastening force without being broken. In this case, when the size difference between the (a) and (a′) increases at least 20%, there may be a limitation of realizing the slim design of the rebar coupler 10.

Since the rebars 20 are strongly pressed after the rebars 20 are coupled to the rebar coupler 10, the rebars 20 may be damaged when a contacting surface between the coupling piece 100 and the rebar 20 is narrow, and a damage (slip) of the rebar 20 and a defect of an operation of the rebar coupler 10 may occur at a tensile strength equal to or less than an authorized tensile strength. In testing of a strength of the rebar coupler 10, a base material (rebar) is required to be fractured at a region other than an inner portion of the rebar coupler 10, so that a fracture of the rebar coupler 10 caused by damaging of the rebar 20 positioned at the inner portion of the rebar coupler 10 may be considered as the defect. Therefore, the rebar coupler 10 is required to be strongly pressed without damaging the rebar.

A length of the coupling piece 100 that does not result in damage to the rebar 20 may be derived from a relational expression (3) from a relationship of (yield strength of rebar)=(tensile load of rebar)*(cross-sectional area of rebar), and a result of an actual test is shown in Table 2.

a+b+c+a′+b′≥0.5×(Length of circumference of cross-sectional area of rebar)   Relational expression (3)

TABLE 2 a + b + c + a′ + b′ value (mm) Fractured portion of rebar D22: Nominal diameter of rebar during performing tensile (22.2 mm) test of rebar coupler 0.3 * 20.9 Rebar inside rebar coupler (circumferential length of cross- sectional area of rebar) 0.4 * 27.9 Rebar inside rebar coupler (circumferential length of cross- sectional area of rebar) 0.5 * 34.9 Rebar (base material) (circumferential outside rebar coupler length of cross- sectional area of rebar) 0.6 * 41.8 Rebar (base material) (circumferential outside rebar coupler length of cross- sectional area of rebar) 0.7 * 48.8 Rebar (base material) (circumferential outside rebar coupler length of cross- sectional area of rebar)

After coupling the coupling piece 100, the housing body 200, and the rebar 20, the coupling piece 100 may be positioned as far forward as possible toward the rebar inlet port 210, and the first concaved region 130 may be positioned apart from an inner circumferential surface of the housing. A part of the first inclined portion 111 of the first protruding region 110 and a part of the third inclined portion 121 of the second protruding region 120 in which the coupling piece 100 and the housing are in contact with each other may be designed to minimize an influence of a welding for coupling the housing body 200.

When the rebar 20 receives the largest tensile force, the rebar 20, positions of the coupling pieces 100, and centerlines 1 of the wall surface 262 of the inner circumferential surface (coupling piece seating portion 260) of the housing in contact with the coupling pieces 100 are as illustrated in FIG. 6.

A dispersion of a force that the tensile force of the rebar 20 is capable of opening the welded portion of the housing body 200 is about 120 degrees. When the welding is performed along a length that is the sum of two base lines of two isosceles triangles around the centerlines 1 that are illustrated, the same fastening force as welding the entire outer circumference of the coupling surface 280 of the housing body 200 may be secured. The sum of the base lines of the two isosceles triangles is obtained by an expression (4).

$\begin{matrix} {{\begin{matrix} {{L + a + b + c + a^{\prime} + d + e} =} \end{matrix}\left( {a + b + c + a^{\prime}} \right)} + {\frac{1}{2}\left( {a^{\prime} - \frac{n}{\tan\theta}} \right)} + {\left( {{3n} - {{a}^{\prime}\tan\theta} + {1.25m}} \right)\tan 60{^\circ}}} & {{Expression}(4)} \end{matrix}$

As an example, a test piece using an SD400 rebar having a nominal diameter of D22 as a base material is manufactured and is tested for cracking of a welded portion when tensile force of 220 kN is applied. The result is shown in Table 3, and it can be confirmed that the coupling of the housing body 200 is maintained without cracking or separation of the welding portion when a minimum welding region (D) that can be referred to as a minimum welding limit line is equal to or larger than 0.85 L.

As illustrated in FIGS. 1A and 1B, the minimum welding region (D) refers to a rectilinear length to the center of the longitudinal direction from the rebar inlet port 210 respectively positioned at the opposite end portions of the housing body 200 including the length of the region of the third step 270 of the housing body 200. The actual welding is performed on the part of the outer circumferential surface of the housing body 200 corresponding to the minimum welding region (D).

TABLE 3 Minimum welding region Fractured portion of rebar coupler during (D) performing tensile test of rebar coupler  0.7 L Welded portion fractured  0.8 L Welded portion fractured No fracture occurred on rebar coupler, and 0.85 L fracture occurred on base material (rebar)  1.0 L No fracture occurred on rebar coupler, and fracture occurred on base material (rebar)

The coupling of the rebar 20 and the rebar coupler 10 that is welded by applying the expression (4) is the same as the view of FIG. 5A, and it can be confirmed that the coupling of the housing body 200 is maintained without cracking and separation of the welded portion even if the tensile force is applied.

Further, as illustrated in FIG. 9, the coupling piece 100 according to another embodiment of the present disclosure may be provided with a second concaved region 140 that is formed by extending from the second protruding region 120, and may be provided with a third protruding region 150 that is in communication with the second concaved region 140, and the coupling piece 100 according to another embodiment of the present disclosure is a preferable structure in terms of further dispersing the force acting on the welded portion. In addition, it may be self-evident that the housing body 200 is further provided with a coupling piece seating portion corresponding to the second concaved region 140 and the third protruding region 150.

The area where the pair of housing bodies 200 is in contact with each other is coupled by welding, and the housing is formed. The housing is configured to accommodate the rebar 20 that is a coupling object in the housing. In the present disclosure, surfaces where the pair of housing bodies 200 is in contact with each other may be coupled to each other by welding, which is different from a conventional rebar coupler in which a pair of couplers are coupled to each other by screwing.

The rebar coupler 10 of the present disclosure may include the housing provided by welding a pair of housing bodies 200 that is two housing bodies 200, and may include the plurality of coupling pieces 100 positioned inside the housing and configured to fasten the rebar 20. Since the housing is formed by coupling the pair of housing bodies 200, the hollows 220 that is two hollows 220 symmetrical to each other and respectively positioned at the opposite sides of the housing with respect to the center of the longitudinal direction of the housing are formed inside the housing, and the pair of coupling pieces 100 that is two coupling pieces 100 may be positioned at each of two hollows 220. That is, the rebar coupler 10 of the present disclosure may be manufactured by positioning the pair of coupling pieces 100 at each of the coupling piece seating portions 260 that are positioned at the opposite sides of one housing body 200 and by welding the area where two housing bodies 200 are in contact with each other after disposing other housing body 200 on the one housing body 200.

Hereinafter, a method of manufacturing the rebar coupler according to an embodiment of the present disclosure, and a method of coupling the rebars by using the rebar coupler will be described. First, the pair of coupling pieces 100 that is two coupling pieces 100 may be disposed on each of the coupling piece seating portions 260 that are respectively formed at the opposite sides of the housing body 200 with respect to the center of the longitudinal direction of one housing body 200. In this case, the first end portion of the coupling piece 100 may be disposed toward the rebar inlet port 210, and the second end portion of the coupling piece 100 may be disposed toward the center of the housing body 200. In addition, at this time, the inner surfaces of the pair of coupling pieces 100 may face each other, and the protruding regions 110 and 120 that are the outer surface of the coupling piece 100 may be in contact with an inner portion of the wall surface 262 of the coupling piece seating portion 260. The coupling piece 100 may be positioned between the third step 270 positioned adjacent to the rebar inlet port 210 and the second step 250 positioned adjacent to the center of the housing body 200.

As described above, after the pair of coupling pieces 100 is disposed on each of the coupling piece seating portions 260, the spring 300 may be fitted between the second end portion of the coupling piece 100 and the second step 250.

Then, when the coupling piece 100 and the spring 300 are in a state of being disposed on one housing body 200, the rebar coupler 10 may be assembled by bringing other housing body 200 into contact with one housing body 200.

Next, by welding and coupling the portion where two housing bodies 200 are in contact with each other, the manufacturing of the rebar coupler may be completed. At this time, the welding coupling may be realized by performing the welding in a predetermined length to the length direction from the rebar inlet ports 210 at the opposite end portions of the housing.

Finally, a user may easily couple the pair of rebars 20 by respectively inserting the rebars 20 through the rebar inlet ports 210 that are respectively formed at the opposite sides of the housing.

By using the rebar coupler according to an embodiment of the present disclosure, a worker may easily couple the rebars regardless of a skill level, and there are advantages that a construction time of coupling the rebars is reduced and the rebar coupler has an excellent fastening strength.

Although the exemplary embodiments of the present disclosure have been described above, it may be understood by those skilled in the art that a variety of modifications and changes may be made without departing from the concept and scope of the present disclosure disclosed within the range of the following claims. 

What is claimed is:
 1. A rebar coupler comprising: a housing formed by coupling a pair of housing bodies to each other; and a plurality of coupling pieces positioned inside the housing and configured to fasten rebars to each other, wherein each of the coupling pieces comprises: an outer surface in which a first protruding region and a second protruding region are provided by being arranged in a direction from a first end portion to a second end portion of the coupling piece, with a first concaved region formed between the first and second protruding regions; and an inner surface provided with serrated protrusions such that an associated rebar inserted into the housing from the first end portion of the coupling piece is prevented from being moved in a direction opposite to an insertion direction of the rebar, wherein each of the housing bodies is provided with concaved spaces that are respectively positioned at opposite sides of the housing body from a center of a longitudinal direction of the housing body such that hollows symmetrical to each other with respect to the center of the longitudinal direction of the housing body are respectively formed at the opposite sides of the housing, and rebar inlet ports are respectively formed at opposite end portions of the housing, and a pair of the coupling pieces is positioned at each of the hollows such that the inner surfaces of the coupling pieces face each other, and the first end portions of the coupling pieces are positioned at inner sides of the rebar inlet ports of the housing such that the rebars inserted into the housing are fastened.
 2. The rebar coupler of claim 1, wherein each of the housing bodies comprises a pair of first steps positioned at the opposite sides of the housing body from the center of the longitudinal direction of the housing body, the pair of first steps being configured such that end portions of the rebars inserted into the housing from the respective rebar inlet ports positioned at the opposite end portions of the housing are in contact with and are seated on the pair of first steps.
 3. The rebar coupler of claim 2, wherein each of the housing bodies comprises: a pair of second steps respectively provided along directions from the first steps toward the rebar inlet ports at the opposite end portions of the housing; and springs respectively interposed between the second end portions of the coupling pieces and the second steps.
 4. The rebar coupler of claim 3, wherein each of the housing bodies is provided with opening portions where the respective springs are partially exposed, the opening portions being configured such that respective end portions of the second steps become respective first side surfaces of the opening portions.
 5. The rebar coupler of claim 1, wherein each of the housing bodies is configured such that an inner portion thereof is provided with coupling piece seating portions that are formed in shapes corresponding to the outer surfaces of the coupling pieces, and the first end portions of the coupling pieces are respectively positioned on the coupling piece seating portions and are respectively arranged in directions toward the rebar inlet ports of the housing.
 6. The rebar coupler of claim 1, wherein when each of the coupling pieces is viewed in cross-section, from the first end portion of the coupling piece to the second end portion of the coupling piece, the first protruding region is provided with a first inclined portion having a predetermined angle in an outside direction, a first horizontal portion extending from the first inclined portion in a horizontal direction, and a second inclined portion extending from the first horizontal portion and having a predetermined angle in an inside direction.
 7. The rebar coupler of claim 6, wherein each of the housing bodies is configured such that third steps are respectively provided at the inner sides of the rebar inlet ports, and a space where the first inclined portion of the coupling piece and an associated third step are not engaged with each other when the first end portion of the coupling piece and the third step are in contact with each other is formed between the first inclined portion of the coupling piece and the third step.
 8. The rebar coupler of claim 6, wherein when an angle between the first inclined portion and an extending line directing toward a first end portion of the horizontal portion is referred to as θ, a horizontal length of the first inclined portion is referred to as a, and a height of each of the serrated protrusions of the inner surface of the coupling piece is referred to as n, the first inclined portion of the coupling piece and the serrated protrusions of the inner side of the coupling piece satisfy a relational expression 1 that is described below. a×tan θ≥1.1×n   Relational expression (1)
 9. The rebar coupler of claim 6, wherein the second protruding region is configured to have a third inclined portion having a predetermined angle in the outside direction toward the second end portion of the coupling piece, and a second horizontal portion extending from the third inclined portion in the horizontal direction.
 10. The rebar coupler of claim 9, wherein the rebar coupler satisfies a relational expression 1 that is described below. a×tan θ≥1.1×n   Relational expression (1) where n is a height of each of the serrated protrusions and a is a largest value among a horizontal length of the first inclined portion, a horizontal length of the third inclined portion, and a horizontal length of an inclined portion of a wall surface of a coupling piece seating portion corresponding to the third inclined portion.
 11. The rebar coupler of claim 9, wherein when a horizontal length of the first inclined portion is referred to as a, a sum of a length of the first horizontal portion and half of a horizontal length of the second inclined portion is referred to as b, a sum of half of the horizontal length of the second inclined portion and a length of the first concaved region is referred to as c, a horizontal length of the third inclined portion is referred to as a′, and a length of the second horizontal portion is referred to as b′, the protruding regions and the first concaved region of each of the coupling pieces satisfy a relational expression 2 that is described below. a+a′>0.1(b+c+b′)   Relational expression (2) 